Every time I post a radio telescope image of a near-Earth asteroid, I get at least one reader question asking me to explain how radio telescopes take photos, so I'm hereby writing a post explaining the basics of how delay-Doppler imaging works.
That's a bit of an overdramatic title, but it's true that the most efficient way for us to reduce the risk we face from asteroids that have a very small chance of hitting Earth in the future is to determine their orbits more precisely.
It was January of 2004 when the elegant curve of the Vichada first caught the attention of geologist Max Rocca of Buenos Aires. Could the course of the river have been shaped by the circular outlines of an impact crater? Rocca decided to find out.